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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Isomerization and fragmentation reactions of gaseous phenylarsane radical cations and phenylarsanyl cations. A study by tandem mass spectrometry and theoretical calculations
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Isomerization and fragmentation reactions of gaseous phenylarsane radical cations and phenylarsanyl cations. A study by tandem mass spectrometry and theoretical calculations

机译：气态苯基ar烷自由基阳离子和苯基砷烷阳离子的异构化和裂解反应。串联质谱研究和理论计算

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摘要

The unimolecular reactions of radical cations and cations derived from phenylarsane, C6H5AsH2 (1) and dideutero phenylarsane, C6H5AsD2 (1-d2), were investigated by methods of tandem mass spectrometry and theoretical calculations. The mass spectrometric experiments reveal that the molecular ion of phenylarsane, 1(.+), exhibits different reactivity at low and high internal excess energy. Only at low internal energy the observed fragmentations are as expected, that is the molecular ion 1(.+) decomposes almost exclusively by loss of an H atom. The deuterated derivative 1-d2 with an AsD2 group eliminates selectively a D atom under these conditions. The resulting phenylarsenium ion [C6H5AsH](+), 2(+), decomposes rather easily by loss of the As atom to give the benzene radical cation [C6H6](.+) and is therefore of low abundance in the 70 eV EI mass spectrum. At high internal excess energy, the ion 1(.+) decomposes very differently either by elimination of an H-2 molecule, or by release of the As atom, or by loss of an AsH fragment. Final products of these reactions are either the benzoarsenium ion 4(.+), or the benzonium ion [C6H7](+), or the benzene radical cation, [C6H6](.+). As key-steps, these fragmentations contain reductive eliminations from the central As atom under H-H or C-H bond formation. Labeling experiments show that H/D exchange reactions precede these fragmentations and, specifically, that complete positional exchange of the H atoms in 1(.+) occurs. Computations at the UMP2/6-311+ G(d)//UHF/6-311+ G(d) level agree best with the experimental results and suggest: (i) 1(.+) rearranges (activation enthalpy of 93 kJ mol(-1)) to a distinctly more stable (Delta H-r(298) = -64 kJ mol(-1)) isomer 1 sigma(+) with a structure best represented as a distonic radical cation sigma complex between AsH and benzene. (ii) The six H atoms of the benzene moiety of 1 sigma(.+) become equivalent by a fast ring walk of the AsH group. (iii) A reversible isomerization 1(+) reversible arrow 1 sigma(.+) scrambles eventually all H atoms over all positions in 1(.+). The distonic radical cation 1 sigma(+) is predisposed for the elimination of an As atom or an AsH fragment. The calculations are in accordance with the experimentally preferred reactions when the As atom and the AsH fragment are generated in the quartet and triplet state, respectively. Alternatively, 1(.+) undergoes a reductive elimination of H2 from the AsH2 group via a remarkably stable complex of the phenylarsandiyl radical cation, [C6H5As](.+) and an H-2 molecule.
机译：通过串联质谱法和理论计算，研究了自由基阳离子和衍生自苯基ar烷，C6H5AsH2（1）和双对苯苯基ar烷，C6H5AsD2（1-d2）的单分子反应。质谱实验表明，苯基ar烷的分子离子1（。+）在低和高内部过剩能量下表现出不同的反应性。只有在较低的内能下，观察到的碎片才是预期的，即分子离子1（。+）几乎完全由于氢原子的损失而分解。在这些条件下，具有AsD2基团的氘代衍生物1-d2选择性地消除了D原子。生成的苯基砷离子[C6H5AsH]（+），2（+）会很容易因失去As原子而分解，得到苯自由基阳离子[C6H6]（。+），因此在70 eV EI质量数下丰度较低光谱。在高的内部过剩能量下，离子1（。+）通过消除H-2分子，释放As原子或丢失AsH片段而非常不同地分解。这些反应的最终产物是苯ar离子4（。+）或苯ion离子[C6H7]（+）或苯自由基阳离子[C6H6]（。+）。作为关键步骤，这些片段包含H-H或C-H键形成下中心As原子的还原消除。标记实验表明，H / D交换反应发生在这些碎片之前，特别是发生了1（。+）中H原子的完全位置交换。 UMP2 / 6-311 + G（d）// UHF / 6-311 + G（d）水平的计算与实验结果最吻合，并建议：（i）1（。+）重排（激活焓为93 kJ mol（-1））到明显更稳定的（Delta Hr（298）= -64 kJ mol（-1））异构体1 sigma（+），其结构最好表示为AsH和苯之间的二元自由基阳离子sigma配合物。 （ii）1 sigma（。+）的苯部分的六个H原子通过AsH基团的快速环行转移成为等效的。 （iii）可逆异构化1（+）可逆箭头1 sigma（。+）最终扰乱了1（。+）中所有位置上的所有H原子。为了消除As原子或AsH片段，倾向于使用离异基自由基阳离子1 sigma（+）。当分别以四重态和三重态生成As原子和AsH片段时，计算是根据实验上优选的反应进行的。另外，1（。+）会通过苯基亚砷二基自由基阳离子，[C6H5As]（。+）和H-2分子的显着稳定的配合物，从AsH2基团中还原H2。

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